Corresponding author: Shih-Yi Hsiung
Abstruct
I obtained the ultrastructure and the macrostructure of pollen grains of 23 modern oak species (Quercus sp.) in California using scanning electron microscope (SEM) and light microscope (LM). These pollen samples were collected from living trees in the UC Botanical Garden at Berkeley and the Tilden Regional Park at Berkeley.Quercus pollen is treated as an important high temperature indicator in the paleopalynological samples. However, the genus is difficultly identified into species level under light microscopy. Here, I provide the results of ultrastructure and macrostructure investigation of Quercus pollen grains for the future palynology studies. Three types of surface texture were recognized in the modern samples with 60 SEM images. The light microscope (LM) investigations of 710 modern Quercus pollen specimens are reported for comparison. The measurements include one size measurement, polar axis and equatorial axis, and two shape measurements, P/E ratio and p/D ratio. I applied T-test on 20 species (excluding hybrid Quercus ,Chrysolepis , and Notholithocarpus ). The results suggest that there are significant difference between sizes and shapes of each species, each section, and evergreen-decidous oaks. Then I applied Moran’s tests on 20 species to test phylogenetic signals. There is only the length of polar view passed Moran’s test (p <0.05;p = 0.041 and 0.042 in 2 tests) when I tested 20 species at the same time. It suggested that the length of polar view of the oak pollen grains contain phylogenetic signals. I also found phylogenetic signal in the distance between 2 furrows in Lobatae sections, Q. agrifoliaQ. kelloggiiQ. parvula, and Q. wislizeni (p <0.05;p =0.035). Further investigations will be focused on details of surface ultrastructure and trait-environment relationships.